text:
Why did early 747s have only two or three windows on the upper deck on each side?
All 747-100s and some 747-200s were built with just three windows on each side of the upper deck.[1] I'm wondering why so few?
Some of the 100s were retro-fitted with ten windows on each side, so clearly the reason isn't structural; nor do I imagine the cost difference would be relatively very much. It seems connected with the original use of the upper deck as a 'lounge' area, but it seems surprising that you'd want a premium area with very little natural light. On occasion Pan Am seems to have been content with just two windows each side.
Was the three-window configuration purely driven by aesthetics, or were there other considerations by Boeing or the airlines?

3-window Pan Am 747-100 upper deck source

10-window Quantas 747-200 upper deck, 1971 source
 source
Pan Am 747s 1969

It's like dark tinting on limo windows - You want people to know you're riding first class, but you don't want them to actually know who's in there.

Different customers have different tastes.  What sort of actual answer are you looking for?  Because unless you are lucky enough that a couple people from Boeing, PanAm and Quantas from that time period frequent this site I don't think you will get anything definitive about why certain stylistic design decisions were made...

I don’t think very many 747-100s had the 3 windowed upper decks.  I think it was changed early on to the ten windowed design.

Early on in the design and development of the aircraft the function of the upper deck changed throughout the early life. Windows are high stress areas and if they can be avoided they typically are. Juan Trippe was a major figure in pushing the 747 into production but during the SST race it was his view that the 747 would largely be a freighter holding the crew on the upper deck. Generally freight aircraft do carry small crews and were likely the original reason for the windows.

Boeing was competing for a supersonic transport contract in 1965, at
  about the same time the 747 was conceived, and Pan Am founder and
  chairman Juan Trippe believed that the big subsonic jets would end up
  as freighters and that the SST would replace the 747 on passenger
  routes. Trippe was one of Boeing’s best customers and usually the
  first to order new models, so Boeing put the flight deck of the 747
  above the passenger cabin to give the aircraft a hinged nose for a
  front-loading cargo door.

The original bubble deck was much smaller but created too much drag and was ultimately elongated. This left dead space that Trippe and his team drove Boeing to turn into a lounge/bar akin to the 377 Stratocruiser's area. Bar's rarely have windows on the ground so why have them in the air...

The first design for the cockpit enclosure was a hemispherical hump
  atop the fuselage. This produced too much drag, so Boeing extended the
  aft portion of the hump to form a teardrop. Then, in a deliberate echo
  of the below-deck lounge on the model 377 Stratocruiser, Boeing’s
  1940s flagship, Trippe and his colleagues persuaded Boeing to turn the
  extra space behind the cockpit into a bar and lounge.

It was not until almost a decade after its introduction during the '73 fuel crisis that airliners started using the upper deck for full passenger seating. This likely lead to the later models having full window treatment of the upper level.

The party days ended with the 1973 fuel crisis, when virtually every
  747 operator got rid of the lounge and replaced it with more seats for
  paying passengers. In announcing the change, a British Airways press
  release noted that the upstairs area was “currently used for a
  first-class lunge”—the spelling was probably appropriate more often
  than not

According to this article:

The first version of the 747, the 747-100, was originally distinguished by an upper deck passenger lounge with just three windows. Later, Boeing offered an option that replaced the lounge with more seats (and additional windows).

As you can see in your first image, the lounge had couches with their back to the fuselage. Most passengers wouldn't be in a position to look out the windows.


text:
What is the non-projected cross-hair for on the F-18 HUD?
Top right, there's a little cross-hair - it looks like it's for lining something up, since on the second pane there's a little dot.
I haven't seen this on any other HUDs. Appears to be present on all variants including Super Hornet.

source

simulated - source

Interesting.....,

It is a "Standby Reticle":

A fixed standby reticle (Figure 7–151) is available in the upper right side of the HUD for use in performing visual designations in the event of a HUD failure. The reticle is fixed at a 15-mil depression angle from the gun boresight. If the HUD fails, the HUD symbology is available by selecting HUD via the menu on the left or right DDI [Digital Display Indicator]. To perform a HUD designation in the NAV or A/G [Air/Ground] mode when the HUD is inoperative, the pilot first places TDC [Target Designator Control] priority to the HUD (either by placing the sensor switch to the normal HUD position, or to the left or right DDI displaying the HUD symbology). The mission computer slaves the radar in AGR mode to the LOS [line of sight] of the HUD standby reticle. The pilot maneuvers the aircraft to position the standby reticle over the aim point and actuates the TDC to perform the designation. The aim point position at the LOS of the standby reticle is computed. The pilot may use the HUD display on the left or right DDI to null the steering error when automatic weapon delivery is being conducted.

Source: ED Forums
The standby reticle is used when the HUD fails for designating targets. The pilot must lean to the right and line up the cross-hairs with the dot so that the bore-sight is accurate.

It is technically the standby reticle as mentioned above but in house it is known more as the seat height marker due to that being the most common use for it.
As soon as you apply battery power the pilot will adjust their seat height lining this up.
Short guys and girls need not lower the seat.
Taller people lowed the seat quite a bit.
You must always check the leg restraint line anchor points are flush with the floor so they don't pierce the rocket motor of the ejection seat.
The HUD is not a display that fails that often so not many people know what this thing is for.
The fact that you can just bring up the HUD page on any of the other displays when it fails and beyond visual range weapons being the default way with regards to tactics means it is seldom used.
Can't give any references as the publications are restricted, but I was a maintainer on this aircraft for over 10 years.

Great insight. Thanks for answering, welcome to [aviation.se] and thanks for your service!

That point and the dot is to know the correct position of the seat height, you must regulate the seat height until you visually match the Cross and the point.

This seems to disagree with the other answer. Do you have a source?

Do you have any sources for your claims?

@Bianfable he has a source now!

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sort: votes


text:
Is 'bouncing' an airliner on landing in high winds a deliberate technique, or something always unexpected?
Last week, 767 landing at Newark, high winds, a good deal of rocking in the last few minutes, some passengers quite distressed. The landing was harder and noisier than usual, and we immediately floated upwards, must have been a couple of seconds before we landed again.
The question I have is - in these circumstances (high winds), would the pilots have been flying the landing with a little less flare than usual and anticipating the bounce as a way of shrugging off some speed / energy; or, is it something you never quite know if it's going to happen or not, and would rather didn't happen at all?

Firm landings are entirely intentional in strong winds, as the answers say though, the bounce is not.

The "noise" may have been the reverse thrust of the jet engines working a little harder.  Bouncing up a few feet isn't perfect, but it is one reason the main gear is supported by the strongest part of the plane, the wing spar structure.

Bounces are bad news on airliners because you are becoming  airborne again just as the lift dumpers pop out, which makes the second touchdown even more exciting and often leads to hard landing inspections, and in extreme cases broken gears.
The lift dump spoilers are supposed to limit bouncing tendency, but if you come down hard enough there is so much energy stored and released they don't come out fast enough or they are ineffective initially when they do or on some airplanes they won't even be triggered until the nose wheel is down.
When you have a significant bounce on a jet you aren't supposed to try to save the landing.  It should be "go around - set thrust" and get out of there.  It's called a "Balked Landing" which is a go-around initiated in a low energy state close to the ground.  You MUST get the lift dumpers retracted, or prevent them from coming out, and setting go-around thrust will do that.  You may touch down again and probably will, but you are supposed to continue with the go around.
There was an Air Canada Jazz RJ that bounced on landing and they tried to save the landing, but the bounce was so high and the lift dumpers were out so they collapsed one of the main gears on the second landing.
Like everything, there are nuances; a little skip, maybe only one gear touched, maybe they feel a balked landing procedure is more dangerous in gusty crosswinds than just landing, so a lot of crews will try to save it.  So maybe this crew did a bad thing, maybe not.  Without a lot more details, hard to say.

So the second landing is the pancake if the spoilers deploy.  The Space Shuttle used a much shorter nose gear to make sure AOA was insufficient for flight while it was rolling out.  Seems spoilers and reverse thrust could wait until mains were definitely down.  I would build 5 mile runways for you all.

Most airplanes only require both mains to be on the ground, plus several other parameters to be satisfied, weight on wheels, wheel speed, thrust at idle, fan speed near idle, etc in various and/or combinations for ground spoiler deployment.  Another big no-no in jets is landing with power ahead of idle. If they are too far foward, the GLDs may not come out at all, and if you skip and then go "oops" and pull them back, enough other parameters may still be satisfied to make them deploy while you are several feet in the air and you'll come down hard.

The bad on is when the nose gear slams and the plane starts to "porpoise". Generally a bounce is handled simply by allowing a little more air speed to bleed off, with gradual increase in yoke back pressure as it does.  End of the runway with large/heavy would be a concern.

If you touch nosewheel first, you are by definition way too fast.  You can handle bounces on regular airplanes that way, but not on airplanes with lift dumpers.  It's straight to the Balked Landing procedure for anything significant.

Bouncing a landing is neither intentional nor desirable. There are several reasons why a student pilot might bounce, but for a professional pilot, it's most likely related to wind gusts, which are a challenge no matter how much training and experience you have.
Gusts are by their nature unpredictable, and if one hits the plane right as it's touching down, it can suddenly lurch upward and/or downward, resulting in a bounce. That's probably also why your plane was "rocking" before landing.

It's a problem with physics.  Since your wings are generating lift, if a gust of wind hits the right way, then you will have a sudden change of lift that the pilot cannot respond to.

bouncing is not desirable - I'll say: https://youtu.be/_wpOkUUCoZ8

Skip to 1:10 in that video unless you have a thing for looking at clips of heavy fog.

The reason an aircraft "bounces" on touch down is that it is going too fast to "settle" on the runway.  Bouncing is far better than "pancaking" from 15 feet off the ground because you were going too slow.  The difference is only a few knots in airspeed, especially for light GA aircraft.
Landing in gusty or variable winds will never be a perfect science.  A light bounce only means the pilot erred on the side of caution, with plenty of runway to do it.

A 767 is hardly a "light GA aircraft".

R/C is another notch down.  Larger mass to S/A ratio would allow for finer speed control in wind. Agree that bounce is undesirable.  Good management of it definitely is.  Still think if they can build thousands of miles of rail road track and interstate highway, they can give pilots a few more feet of runway.

@RobertDiGiovanni I hear you about a few more feet - my dad was a pilot in the RAF in the 1950's and 1960's, with numerous landings at Hot and High locations in the middle east and Africa.  He told of some hairy episodes at both Nairobi and Salisbury (now Harare) flying a Bristol Britannia.  The main issue in some places is finding the space.  Take a look at San Jose airport on Google maps - there's simply no room for another foot, not with those freeways at both ends of the runway.

@dgnuff And that's why we have EMAS. :)

Usually bouncing is completely undesirable, because this will increase your landing distance quite significantly to the extend you might overrun the runway if you don’t go around.... so better avoid it...

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text:
What is this aircraft (Le Bourget airshow 1965)
Approximately 31 seconds into this video of a walkaround of the 1965 Paris airshow, there's a curious aircraft shown next to a Navy F-4.

The question is - what is it?

It's a Nord 500 Cadet. From Wikipedia:

A model kit presenting the concept was first shown at the Paris Air
  Show at Le Bourget in 1965. The aircraft was driven by two ducted
  fans, with three blades per fan, mounted on short wings that were able
  to pivot between providing vertical and horizontal thrust.
Two prototypes were constructed, one making its first (tethered)
  flight in July 1968.

This early VTOL concept aircraft was designed by Nord Aviation (formely Potez), the French manufacturer. They were known for their military Transall and Noratlas seen everywhere in Western Europe in the 60s.
This aircraft is similar to CL-84 and XC-142 designed at the same period. The only one to have flown:

(Source)

(Source)

Powered by Allison T63 (aka Model 250) turboshaft, 316 hp.
Maximum speed: 350 km/h.
Ceiling 4,101 ft.

The prototype used for static demonstration:

(Source)

Bonus: Trying to fly the prototype on Youtube.
A quite funny video I may say. With nearly all the attributes of my fellow countrymen of this era: beret, cigarette... just missing a baguette under the arm.

gets away with stereotyping by being one of "them"  :)

And I thought the coléoptère was the most ridiculous plane from Nord...

"Ceiling 4,101 ft." - What an odd ceiling.  Is that a typo?

@WayneConrad: French don't use ft in engineering, it's 1,250 m

@mins Thanks.  It say "ft." in the answer, but I can't change it to "m" because it's too small an edit.

@WayneConrad: I meant 4101 ft comes from a conversion of 1250 m, the ceiling was translated from original m to usual ft in the answer.

That makes more sense.  It must have been very power limited with a ceiling so low.


text:
Boeing 757-200 Fuel Burn
So up front, I'm aware of the high number of aircraft and environmental factors and how oversimplified my request is. After all, there is a reason that the aircraft manufacturers provide charts to calculate such things, and not hard numbers.
I'm looking for the average fuel burn rates for a Boeing 757-200 at MTOW during the first hour of flight, and then the same, the average fuel burn rate for the second hour of flight. If you have a range for each period, that be cool as well. If you need variables to run the calculation, I offer the following:

Field Elevation: 1,000' MSL

Temp: 59° F/ 15° C Altimeter Setting: 29.92 In-Hg/ QNH 1013 Final
Cruising Alt: FL380 Assume standard takeoff configuration and initial climb performance. Standard cruise climb t FL380 with no clearance altitude restrictions or ATC level offs

I think that's it, let me know if I forgot something.

Did you have a chance to look at this answer? Repeat the same for the (rather similar) 757, and you have your numbers. Only the climb phase in the first hour will need special treatment.

Thanks Peter. I think the B757 burns appreciably more fuel than an A320, in fact I believe it's around 1,000 kg/hr more at MTOW. Still, I appreciate the suggestion.

Of course it does, when you look at the absolute numbers. They scale linearly with weight. What you should  look at are the relative numbers given in that answer; they should be very similar for the 757.

Ahhhh, ok, thank you!!


text:
Why do many aircraft have both all-moving tailplanes and elevators?
Many aircraft - particularly large commercial airliners - have both an all-moving tailplane (horizontal stabiliser) and elevators. (They also have a small third moving element on the trailing edge of the elevators too.)
As far as I can tell, all these surfaces do exactly the same thing, ie cause a change a pitch. Indeed this answer confirms that both stabiliser and elevators have the same effect, although hints there may be differences at transsonic speeds, something that doesn't apply to most airliners.
I understand trim is concern, but ultimately you're just trying to point the nose up or down. Especially with computers calculating optimum angles, having two control surfaces, which may counteract each other, seems to add a lot of complexity.
Of course there must be some advantage to having both, I'd like to know what that is?
 737 empennage (source)

would this answer help?

Moving each part has different effect on drag:

Moving just the elevator increases camber, producing large force which is useful for manoeuvring, but it also produces more drag.

Moving the whole stabilizer, keeping the camber low, produces less drag for the same force, which is good for cruise efficiency.

That's why the elevator is used for control and the forward part of the stabilizer for trim.

The arrangement adds complexity, but it also adds redundancy. If one of the actuator breaks and jams, the aircraft is still controllable using the other part enough to make a safe landing.

This, plus trimmable stabilizer allows full elevator deflection with all trim settings.

@busdriver, full deflection, but not full authority, since the stabilizer and elevator commands are approximately added together.

Never thought much about needing a supercritical tail plane too, but yes, a cambered tail plane would be a disaster in transsonic flight.

Drag is one main reason, as outlined in @JanHudec's answer; the other one is maneuverability given the fairly wide CG range that exists on modern transport category aircraft. Without horizontal stabilizer, elevator may be insufficient for maneuvering at forward CG.
One probable limitation would be the compliance with 14 CFR 25.107(e)(3) and (4), where prompt takeoff rotation must be demonstrated in all-engine-operating (AEO) and one-engine-inoperative (OEI) condition with rotation speed below $V_R$ (-5kt for OEI and -7%/10kt for AEO) at maximum takeoff weight and most forward CG. Prompt rotation may not be achievable with a fixed stab angle and full nose-up elevator.
Another one may be the ability to demonstrate stall speed as per 14 CFR 25.201, with flaps down at forward CG. If the lowest speed reached is limited by pitch authority, then that would be the lowest speed a manufacturer can declare, regardless of how low the actual aerodynamic stall speed is. This negatively affects the field performance.
Having a trimmable horizontal stabilizer solve or, at least, greatly mitigate, the above-mentioned issues. The cost, as you mentioned, is greater complexity and additional failure modes to consider. For example, compliance with 14 CFR 25.107(e)(4) will now also need to demonstrate prompt rotation with the maximum mistrim of the h-stab on takeoff.

How did the TriStar handle compliance with the Part 25 requirement you mentioned? That might be instructive...

@UnrecognizedFallingObject I can't find much authenticated information about the L-1011 FCS, beyond that it has a (perhaps) stabilator and (geared) elevators. If you have any sources, would love to learn more.

My understanding is that the L-1011 used an all-flying, hydraulically controlled horizontal tail with geared tabs on the trailing edge, yes, but I don't have sources handy either sadly :/

Related - stabilators are aerodynamically required for super sonic fighters to maintain elevator authority. Interesting history to read about its discovery and Chuck Yeager. If I recall correctly, it boils down to trim tabs do not work and can kill you once you exceed the speed of sound due to the shock wave propagation.
For general aviation, which do not use fly by wire, a stabilator provides greater elevator control because less physical force it required for movement. It is typically augmented with an anti servo.
Google Mach tuck, stabilator and antiservo for interesting materials both basic and technical.

we don't send people to google, we provide complete answers here, or we directly link to relevant documents.


text:
Where are jack points typically located on an aircraft?
I realised that full gear swing tests require an aircraft to be fully jacked up; and I think it would make sense to locate the jack points close to the landing gears themselves, on the same load-bearing structures (e.g., main wing spar), since those structures are already designed to support the weight of the aircraft.
Is that generally the case, and are there considerations where designers would locate the jack points elsewhere (and presumably have to specially reinforce these other locations)?

You would also need to consider the bulk of the jacks and make sure the gear (or the panels) won't hit them on swing test.

Yes indeed, at strong points such as landing gear structure, engine support, or wing strut. The jacks need to be out of the way of the swinging doors of course, but as close as possible to the fuselage.

This one has a special design man leg jack.

Close to the fuselage - presumably to reduce bending in the wing? Thanks for including different examples like the high-wing and the GA plane supported at the tail. I also noticed one of them used a plate to distribute the weight, while others seem to do fine with a smaller contact point.

Yes to reduce bending in the wing. The wing normally supports the aircraft in flight, but the force is neatly distributed over the area of course, with relatively more air pressure  near the root. The landing gear is the only spot in the wing that is designed for concentrated full force, with the aircraft coming down at 10m/s/..

Smaller planes have relatively over-dimensioned skin due to the sheet metal having to have a minimum thickness for workability etc, placement of the jacks does not seem very critical there. I've used aircraft jacks to jack up flight simulators for installing them on their motion base but that is a steel frame, some of the practices i've seen with GA aircraft make me nervous. Wood always seems a good idea

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text:
How is fuel ignited in jet engines?
From what I understand, in jet engines, air is compressed and fuel is not only injected but also ignited : how is this done ?

Are you asking about when an engine is first started, or when it is already running?

@BowlOfRed : when it is already running

Ah yes, I think so ! I will try to learn a bit more about auto-ignition temperature. Thanks a lot @BowlOfRed !


text:
Where can I take ICAO Aviation English proficiency test?
Do you know some pages which listing the place I can take ICAO Aviation English proficiency test or useful pages?
I sent e-mail to ICAO and search it many times. But, still I can not obtain good information.

ICAO doesn't issue licenses or do training directly, their member countries do that. That means the best idea is probably to contact the aviation authority of your country, but if you can tell us which country you're in then someone may be able to help.

Then, I can understand there are no  lists. USA or Asian countries like Taiwan, China, Hong kong, Japan will work for me.

There is no central list. Many places that offer international flight training also offer Aviation English courses. Check out whichever ones are near you.

ICAO does not offer testing or training itself, only sets standards that most countries adopt (sometimes requiring stricter even) as their own.
The relevant aviation authorities in your country might have such a list of places authorised to offer the test, if you can't contact them directly any flight school will be able to assist either directly or by bringing you into contact with another school that offers theory classes.
E.g. in the Netherlands EASA rules apply, which sit on top of ICAO rules, and are enforced by the Dutch ministry of transportation. Examination is handled by the CBR (which also handles drivers' licenses). Schools offering theory classes can enroll you in the exams and tend to have the facilities to take the exams (which are all remote/computer based these days, in the past you had to make your way to one of a very small number of offices on a limited number of available exam days each year).
Similar arrangements are to be expected in other countries.

Thank you. I'll contact the relevant aviation authorities!

I don't know where you are from, but if you are near Germany, "Lufthansa Aviation Training/European Flight Academy" conducts these tests on a regular basis. Just give them a call and maybe you can participate in one.


text:
How do dummy bombs simulate real bombs in training when they're so much smaller?
This picture shows a couple of Mk-76 25lb (11kg) Inert Training Bombs on a McDonnell Douglas AV-8B Harrier II; it's clear that the physical characteristics of the dummy bomb are quite different to actual munitions.

source
The manufacturer says these bombs are "used to simulate the MK-82 in low drag configuration". The venerable Mk-82 is typically 500 lb (227 kg): here's an F-16 with Mk-82s for scale comparison:

source
One obvious advantage of the smaller, lighter bombs is that they're vastly cheaper to operate, both in terms of handling on the ground and the amount of fuel you'd be using in the air. However, the dummy bomb is 20 times less massive than the bomb its designed to simulate: its small size and weight surely mean their aerodynamic characteristics are very different to the bombs they're supposed to be simulating. (I know that speed of fall in a vacuum is not dependent on weight, but a falling object in air is affected by shape, weight, drag etc.)
My question is - since their purpose is presumably to help train the pilots, how can tiny dummy bombs usefully simulate real bombs?

"surely mean their aerodynamic characteristics are very different" really?

This goes way back Galileo's famous gravity experiment (later quantified by Newton). I'm surprised that people still don't know that things of different sizes all fall at the rate of 9.8m/s/s. If you're worried about aerodynamics characteristics that has nothing to do with size or weight - a grain of corn is roughly the same size and weight as a feather but their aerodynamics characteristics are completely different. On the other hand a model 747 is hundreds of time smaller and lighter than the real plane but their aerodynamics characteristics are basically the same

@slebetman - Thanks - as I said in the question I'm aware of the very basics of gravity, but "things of different sizes all fall at the rate of 9.8m/s/s" is just not true (in Earth's atmosphere), e.g. a beachball and a cannonball, or a penny and a skydiver.  For all these things their initial acceleration decreases to zero at different rates, and their terminal velocities are different too. Hence the question.

The actual mass alone is nearly irrelevant to its a trajectory - what mostly matters is the mass/drag ratio - so if you scale the drag correctly, it feels quite the same - at least from the operational point of view. As one does not drop bombs by sight only, a small adjustment on the computer will do the other trick.

I guess this is common, when munitions are rather expensive [citation needed]. There is a sub-caliber training device for the RPG-7, which fires a 7.62 mm bullet, from a dummy grenade. Here is a discussion from the ForgottenWeapons YouTube channel.

Provided the bomb has the same ballistic characteristics, the mass of the bomb would be irrelevant to this.  Now the weight of the actual MK82 series 500lb bombs may have a distinct effect on the maneuvering characteristics of the attacking airplane during a bombing run as opposed to carrying a load of MK76 ‘Smurf Killers’ to a target.


text:
What features enable the Su-25 Frogfoot to operate with such a wide variety of fuels?
It is widely attested* that the Su-25 Frogfoot's engines (the Turmansky R-95Sh and later the R-195) were designed to function using a wide variety of fuels, including diesel, gasoline, petrol, kerosene and avgas.
For a rough-field front-line attack aircraft, the ability to load it with whatever was at hand, even tank fuel, would be very useful.
It's not a feature I've read about anywhere else. The question is, what specific engine modifications allow this level of fuel-tolerance in comparison with, for example, the T-34 which powers the A-10, an aircraft designed for a similar role.
 * for example miltaryfactory.com lowflying.net
 Su-25 Grach  (NATO reporting name: Frogfoot)

(Previous questions asked whether diesel engine aircraft can run on car diesel (yes) and if you could safely run a 777 on diesel (no).)

Gasoline and petrol are the same thing.

Ah but do the soldiers know that? :)

@Sean One is measured in gallons and the other in liters.

The C130 engines are similar.  In fact, many turbines can run on fuel other than Jet-A.  Put simply, as long as a combustable material can vaporize in the cans and burn without contacting metal, the engine will spin.

Being a ground attack aircraft, the Su-25 has an operational ceiling of 23,000 ft and will not encounter the low temperatures to which a Boeing 777 is regularly exposed. Therefore, the risk of diesel fuel gelling and clogging the fuel lines is much lower.
On the other side of the temperature scale, gasoline could vaporize in hot environments and equally endanger the fuel supply of the engines. Those extremes are rarely found in the countries of the former Eastern Bloc, and the Su-25 was primarily designed for operations in moderate climates.
Nevertheless, some modifications are advised in order to avoid trouble when exotic fuels are used:

Regular fuel pumps use kerosene for lubrication. Kerosene is a good lubricant and allows for a simpler pump design. By using better bearings, the fuel pump can also be used with gasoline or petrol without suffering long-term damage.
Running the fuel lines away from hot surfaces reduces the risk of vapour bubbles forming inside. I don't know the details of the Su-25 design, but I would be mightily surprised if any fuel line runs right below the upper skin of the aircraft where the sun can heat the surface to temperatures in excess of 70°C even in moderate latitudes. This is supported by a light grey paint scheme as shown by the Ukrainian Su-25 in your question.
Don't do fancy things with the fuel, like use it as a hydraulic fluid, but restrict its use to being burned in the engine, and maybe cool some engine oil on its way into the combustor. Then any liquid hydrocarbon can be used.

That turbofans can run on a wide variety of fuels has been established in the answers to this question.

Another factor: military engines aren't made to last very long. This article says TBO is 750-1500 FH. You can just let the pumps and components wear.

@user71659: That is typical for Russian engines, but does not indicate their fragility but the desire of Soviet planners to keep engine mechanics employed. When the West German airforce looked into the East German MiG-29s after reunification, they found that the engines would safely last for almost three times the scheduled hours. The An-70 is designed to last for 6 months without any maintenance (but after that time it is really worn out).

I suspect that you mean 70°C, but it would be great if you clarified.

@chrylis: You're right, thank you for spotting this.

@PeterKämpf The time is still nothing compared to a limit of 30,000 FH on the GE90. It makes sense considering a F-16 airframe is good for 14,000 FH, an engine designed and operated to transport standards would outlast the plane by >2x

@user71659: You're right, military hardware is assumed to not last as long as commercial hardware for obvious reasons. There are inspections inside those 30,000 hours, however, only the engine can remain on the plane during those, so the comparison is not quite on equal terms.

So you are saying that some aircraft do use the fuel for fancy things like hydraulics?

In this video, where the various accessories on the outside of a GEJ79 turbojet (which powered the F4 Phantom, amongst many others) are being identified by a contemporary technician, there is a factory-fitted device to adjust the fuel system to use different fuels.

(at about the 10.30 point)
The F4 saw service with both Navies & Air Forces, which used different fuels due to different operational standards, so adjustment for this was not exceptional. I do not know if the facility for the J79 to use gasoline was ever used in practice; there are a number of serious maintenance consequences of using something like gasoline, so just because it can be used, doesn't mean it's a good idea.
It is common for land-based gas turbines, such as tanks & various stationary applications, to be able to swap between different fuels, although some applications require changes to fuel nozzles etc for efficient operation. Operators of the M1 Abrams tank famously claim that they can run it on anything, from Chanel No5 & bourbon to gasoline & heating oil.


text:
Is this a famous aviator / airplane?
This may be a little off topic but I could not find a better community or website.
I have two photo postcards with a man in front of a plane. Pretty sure it's Charles Lindbergh but an exhaustive Google search for anything related visually has only turned up another picture of CL with a similar jacket on. So is this who I think it is? Can anyone come up with a "verifiable" narrative to accompany these photos? Perhaps the type of plane in the background?

I don't believe it is Charles Lindbergh, Lindbergh has a pretty noticeable divot in his chin, this gentleman does not.

Are you sure that is a plane?

@mins - I think you're getting closer, but the door isn't that wide. The subject of the photo definitely seems to be Chamberlin, and the stamp on the photos indicate they were taken in Boblingen, Germany. The upper part of the stamp is probably the name of the photographer, but I can't make it out... Rich Lummle, maybe?

I couldn't identify the plane, but using the stamps I found the specific date & location of the photos. The plane wasn't his, it was just one he was boarding at the time for a short flight.

@Omegacron: Publisher: Richi Lämmle, Böblingen as here.

BTW, if I were the OP I'd have these photos lovingly framed in glass on my wall. And now that we know the who, when & where, I'd have that info on a little bronze plaque on the frame. And I'd love them, and look at them for inspiration, and growl at my wife if she threatens to dust them off.

I think the plane is a Lufthansa Dornier Merkur airliner.

@TomMcW - I think you're right. Would you mind if I add that to my answer?

@Omegacron Sure

@TomMcW: Maybe the reason is in this article dated June 14: "Early tomorrow morning Chamberlin and Levine will motor to Karlsruhe and will proceed from there by airplane to Friedrichshafen, where they will inspect the Zeppelin and Dornier Merkur Works. They will next visit Stuttgart and Frankfort and will go to Hanover Thursday, and from Hanover to Bremen to meet their wives, who are due Friday from New York on the steamer Berlin." Source.

Good find @mins - now we just need to identify the tail number of that specific plane and we're there! Looks like D14-something (assuming there's a "1" behind him in the top photo), but haven't found a better picture of him boarding yet.

Luthansa had 30 Komets in service, so we know it was most likely one of those. And it looks like those all had a tail number starting with D-1-something.

Correction - the Komet III prototype in 1925 had a tail number of D-815, so that last comment may not be correct.

@Omegacron This site seems to list all aircraft of the type made. Looks like there were several with D-1XXX.

Btw, I totally want a jacket like that!

@mins - awesome find, I'll go through that and see if I can narrow it down. Also still searching for a different angle that shows more of the number.

@Campbell - all joking aside, if those are original postcards and not recent reprints, you should seriously consider ordering a couple of those hard plastic snap-shut cases to protect them. Lots of places online like Amazon sell them, and they're generally pretty cheap. You just need to measure the postcards to get the size right. Stay away from the flimsy clear sleeves as much as possible - you want the rigid plastic ones that snap shut tightly.

Well, I guess I'm giving up on the tail number chase. At least seven of the tail numbers on that list operated out of the airfield at some point, and the number behind Chamberlin could be any of five of those, possibly six (if that's a "7"). Unless someone can find a better picture revealing more of the number, or an article listing the actual flight, I'm stuck.

The pictures are of Clarence Chamberlin, after he landed near Boeblingen in 1927. Thanks to Omegacron for pointing out this website, which also has the exact same picture as the 2nd one you have. https://www.boeblingen.de/,Lde/start/WirtschaftEntwicklung/Chamberlin.html
Notice the similar bouquet of flowers, postcards in his front left jacket pocket, and how his jacket is buttoned.

(gettyimages)

@ymb1, will do that thanks, thought it went without saying. I couldn't find markings on the New York which match the 1st picture (looks like a capital D), so am kind of stumped on that so far.

I gave you a +1 for the find, but that quote is wrong. He was flying the "Miss Columbia" when he landed in Eisleben. He CAME from New York, so maybe that's where the confusion was.

@Omegacron, corrected and sourced, thanks! I would add the matching picture to your post!

Thanks to the research of the other two answers, I finally found the context for these two photos. They are indeed of Clarence Chamberlin (a contemporary of Lindbergh) and were taken on June 15, 1927 at the Stuttgart-Boeblingen Airfield in Germany. The following page describes the events leading up to the photos, although the original is in German:
https://www.boeblingen.de/,Lde/start/WirtschaftEntwicklung/Chamberlin.html
Long story short, he was attempting to beat Charles Lindbergh on the transatlantic record, but Lindbergh won due to numerous delays. Chamberlin decided to go a little further, to Berlin, and beat the distance record instead. There were numerous technical problems with his plane, however (the Miss Columbia), and he ended up having to land in Eisleben, about 90 miles west of his goal on June 6, 1927. After a day spent repairing the plane, he then proceeded to Berlin. The event seen in the photos is a parade/celebration thrown in his honor as he leaves on the 15th.
By comparison, here's a photo from the same event showing Chamberlin in the same clothes:

I was unable to identify the specific plane behind him in the photos, but it was NOT the Miss Columbia. Due to the many technical problems experienced during the race, Chamberlin elected to return by sea. What we see in the photos is him about to board a passenger plane that will take him to the ship. As far as I can tell, the Miss Columbia was shipped back separately, although his co-pilot (and the plane's owner) Charles Levine wanted to fly it back despite the problems.

What About the Plane Type?
The plane that Chamberlin is boarding in the photos looks to be a Dornier Mercury, which was a common passenger plane in Germany at the time. The door size/shape and top of the plane (what we can see, at least) match up quite nicely. Here's a shot of one from a similar angle:

Thanks to @TomMcW for finding that.

You are correct, the 2nd picture is there exactly as well

There's a lot about Lindberg, Chamberlin and Levine in one of Bill Bryson's newer books, Summer 1927, really interesting read. Aviation features heavily. https://www.theguardian.com/books/2013/sep/26/one-summer-1927-bill-bryson-review

(wikimedia)
I may be wrong, but it looks very like Clarence Chamberlin; the Wikipedia picture is quite small, but if you look at some other pictures you can see a very strong resemblance. According to Wikipedia he carried the first transatlantic passenger, flew an aircraft off a ship, and was a famous barnstormer. So there are plenty of reasons why he could have ended up on postcards.
I don't know what the aircraft is. Wikipedia says that Chamberlin's most well-known aircraft was Miss Columbia, a Wright-Bellanca WB-2. But the pictures of it show it has a square door under the wing, whereas your pictures show a rounded door rear of the wing. He was also associated with the "Curtiss Condor CO" (a Curtiss T-32 Condor II?) but again, it doesn't seem to match visually.

Another picture with the same jacket, and another postcard.

@ymb1: Well it's Pondlife 's answer, he decides (he's in charge, he's the boss, the head man, the top dog, the big cheese, the head honcho, number one)

@mins you forgot "el numero uno"

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Does density altitude affect actual altitude?
Student pilot here, working on my first rating. A lot has been drilled into my head about density altitude as we approach the hot summer months here in the northern hemisphere, and how it causes the plane to act as though it were at a higher altitude—less lift, less power, less thrust—but no one seems to understand when I ask if this also puts the aircraft higher in the sky, as well.
As near as I can understand, the atmosphere actually expands and becomes taller under hot conditions, and the various pressures that we associate with certain altitudes are actually further apart. Is there a flaw in my understanding?
It mystifies me that no one I've talked to seems particularly concerned about something that could potentially throw off your ability to judge your true altitude. Wouldn't you need to be more concerned about cold-weather density altitude when crossing mountain ranges? The mountains don't get shorter just because your pressure levels are closer together . . . right?

Do you understand the difference between height and the different types of altitude?  This will help to form an answer.

To be on the safe side, I'm going to say, "no," and hope to learn something.

puts the aircraft higher in the sky

What you are talking about, above your standard altimeter adjustment is altimeter/temperature Error Correction. The article describes when to apply corrections generally speaking and what should be applied. In short pressure altimeters are calibrated for standard lapse rate so if the air temperature changes at a constant rate across an altitude block the altimeter will work just fine. However if you have blocks changing at varying rates you may need to compensate for that.
Generally speaking, the airspace system is designed to prevent this from being an issue. Mountain crossings are done at safe altitudes and when low approaches in such conditions are necessary calibrations are used it may be required to have something like a radar altimeter on board which is not susceptible to this issue.

Density altitude is barometric altitude corrected for nonstandard temperature or pressure.  So the Pilots Handbook of Aeronautical Knowledge says but what exactly does that mean?
First remember that an aircraft altimeter is really nothing more than a very sensitive barometer; it simply translates atmospheric pressure readings into those found at a corresponding altitude above seal level.  Since air pressure drops by approx 1 inHg for every 1000 feet above MSL, a barometric altimeter becomes an effective means to gauge height above sea level or similar reference datum.
Since the atmosphere varies in both temperature and pressure in different places of the atmosphere around the globe, there exists a need for a standard atmospheric condition to be used as a datum of reference.  In SI, this Standard Atmosphere is defined as 1013 millibars (29.92"Hg) at 15°C (59°F) at Mean Sea Level.  This standard atmosphere is also a good baseline to calculate performance data for an aircraft at.  Charts and performance data are usually created based on an aircraft operating in Standard Atmospheric conditions.
But since ambient atmospheric conditions vary in both temperature and pressure, it is convienent to have a means to convert the ambient air conditions and altitude into an equivalent pressure altitude in standard atmospheric conditions.
Hence this is what Density Altitude is.
Note that Density Altitude has nothing to do with your true altitude or absolute altitude; rather it's an equivalent altitude reading which one would see at STP in the current actual altitude, temperature, and pressure of the air you are currently in.
As an example, suppose you are at Lake Co. Airport in Leadville, Colorado.  The field atmosphere here is 9934 ft ASL at 20°C with an altimeter setting of 30.12"Hg.  These condition correspond to one you would encounter in air at standard atmospheric conditions at 12,614 ft ASL or gives us a density altitude of 12,614 ft.  This doesn't change the fact that you are still only 9934 ft ASL while on the ground in Lake Co. but it does give us a means to quickly use the manufacturer's performance data based on STP to determine the aircraft's performance under these conditions.  One would use said charts and compute the performed AS IF the airplane were actually at 12,614 ft at STP versus at 9934 ft in local atmospheric conditions.
Density altitude is of greater importance on hot days than cold ones because the air is less dense when warm than when it is cold.  Since both the lift wings can produce at a given true air speed and the power output of an engine are directly proportional to the density of the air, this results in an aircraft which sluggish, even dangerously deficient performance on hot days with high density altitudes than on cold ones with low density altitudes.

No a hot day does not put you higher in the sky, your altimeter just measures a lower air pressure, one that you would find at a higher altitude on a "standard" day.
Density altitude is just that: altitude measured in air pressure (and therefore density), not in feet. It's a convenient but indirect measure of altitude, depending on what we know about how pressure varies with altitude on a standard day.
On a non-standard day, we measure the same pressure at a different altitude, and this is basically what the instructors are talking about:

the altimeter needs to be corrected for the non-standard temperature and air pressure at ground level.
once this is done, you can find you correct altitude (in feet) at the different air pressure that the instrument is measuring.

Why do we do all this, and not simply just measure altitude directly in feet with a radar altimeter? Because we not only need to know how far away from the ground we are, but also how high other aircraft are, relative to ours, while they're flying over lower or higher terrain.

No.  Density Altitude tells you about the air, and more specifically, how your engine and aircraft, lift, will behave in that air.
To punctuate the point, if your plane is at 20 ft above sea level on a cool day, you are at 20 feet.  At that same airport, on a very hot day, you are still at 20 feet, but your airplane acceleration will be slower, AND you will need a higher ground speed to achieve the IAS needed to take off.
Now, I'll get a little confusing.  I have never liked IAS.  It's not about speed, it is about  pressure.  How much lifting pressure is under the plane.  You have a range of pressures.  The minimum is your rotation speed.  At a certain "air speed", you are moving fast enough through the air to create pressure to lift the plane.  VNE is the maximum pressure your plane is designed to take.
When the air is cool and/or the altitude is low, it is thicker.  You need less ground speed to reach you IAS rotation speed.  When it is hot or high, the air is thinner, provides less lift, so then you need more ground speed to reach your IAS rotation speed.
An illustration of heat, density altitude, happened, last(?) year in Phoenix.  The temp got to 116.  The airport shut down.  Why? Because the jets taking off would have to achieve a higher ground speed to create enough pressure, IAS, under the plane to take off. The takeoff calculations said the jets could not create enough ground speed in the given runway length, to create enough pressure, IAS, to achieve liftoff.
So, again, no. Density Altitude has nothing to do with your actual height above the ground.  It DOES have a lot to do with your speed over the ground.  On a cool day at sea level, if your rotation speed is 80, your ground speed will be 80.  On a very hot day, at the same airport, your ground speed will be higher to achieve 80 IAS.


text:
How many parts does the latest-generation 737 share with the original 737?
There is an old paradox which states that if a boat sails round the world replacing worn out parts as it goes, once it has replaced all of itself is it still the same boat?
I choose the 737 because it's been around for over 50 years. Specifically, is there anything from the original tooling for the 737-100 that would be a straight out replacement for a 737-MAX?
 737-100 source
 737-MAX-7 source

I'd guess that the seats out of the -100 could be used in the -Max but probably aren't because newer ones are (most likely) both stronger and lighter.

Since you restrict the parts considered to those from 737 tooling, is it correct that you exclude purchased common parts like fasteners, wire and tubing?

Hi, what I'm getting at is whether at Boeing or any of the other subcontractors are still making the same part specifically for the 737 that they did 50 years ago. I realise that's a little bit vague, but I'm trying to get a sense of whether the 737 moniker is purely a marketing device or whether there really is some fundamental commonality that has been present throughout its life.

I think you're talking about this ship mate https://en.m.wikipedia.org/wiki/Ship_of_Theseus

@FreeMan ... and less comfortable :P

@TomMcW - you are 100% correct, of course. My apologies, I was making the assumption that there was a base level of knowledge about aircraft among our readers. That probably would have been a safer assumption at [travel.se] than here at [aviation.se]. :D :D

@FreeMan: Well, if you want technical knowledge about aircraft, you're in the right place.  If you want knowledge about what planes are the nicest to fly on, Travel is your place to go.

The cross section and cabin pressure have remained the same. From what I can tell virtually every part is different. Even parts that might have been able to retain the same shape/loading have gotten improved materials and/or corrosion treatments. I am still looking to see whether any window panels could be common as the holes into which they go have remained the same.
Looking at a couple of generations shows major differences, allowing elimination of whole sections of the aircraft. Wings, tail, engines, pylons, landing gear, fuselage center sections, APU, interior and flight deck have all surely changed.
Originally conceived as a 60 seat jet, the first production model was designed for 100 seats.

The Max10 now goes to 230.

The Max also had major improvements to the the cockpit. Even the throttle levers changed. Here is a photo comparison to the original -100 flight deck.

b737-100

b737-max
NG changes, both structural and cosmetic.

larger wing with new flaps slats
larger tail with improved rudder and elevator
simplified higher capacity landing gear
engines
new AC electrical system
new corrosion resistant materials and treatments throughout the plane
new interior seats, panels, bins, coverings
improved avionics

Standard cabin pressure remained the same, but the rated pressure differential increased progressively with each version. This is what affects the structural design most (in this regard).

Only a mechanic with the list of part numbers could tell for sure. My first guess might be the wet compass, or the galley coffee pot. The TCAS control head wasn't original in the -200, but the ones installed in those aircraft might still work in a NG; not sure if a Max needs a different one or not. Some other obscure part might fit the bill, but I don't know what. Roller for the toilet paper holder, maybe? Plastic guards on the guarded switches? Individual switches for things like generators and hydraulic pumps, perhaps.
The commonality is less from the -100/-200 to the Max, as it is from the -100/-200 to the "Classic" series (-300 thru -500) to the NG and then to the Max. For each step, it was a common type rating and fairly quick "differences training". The Max has plenty of switches and conventions that are very close to the -200, just not quite identical. For instance, the Max still uses a Master Caution system, rather than an EICAS. Reason? To maintain backward compatibility to the Next Gen aircraft, which didn't have an EICAS in order to maximize compatibility with the Classics. Likewise, much of the overhead panel would be recognizable to a 737-200 pilot, and nearly identical to a Classic overhead. Not "same part number" identical, but very, very close.
A pilot who has flown both pointed out that the 737 NG is a newer design than the 777, even though the latter when it rolled out 20+ years ago was far more automated than the Max is today!
Certainly not simply a marketing device but very real similarities and roots to the past. I doubt many parts from a 50 year old Corvette would fit a brand new one, either, but that doesn't deny the lineage dating back to the original!

The 386 lightbulbs are probably common to both. They're probably made slightly differently today than they were in the 1960's, but a 386 bulb from a 737-100 would almost certainly work fine in a Max, and vice versa. Those bulbs are used in the various indicator lights in the overhead and front panels.

I read "386" and thought "Intel 80386" and was really confused. /feeling old

I would guess that some structural elements of the airframe might not have changed much, since the basic fuselage geometry is unchanged (except for stretching), right?

@CptReynolds although the general shape hasn't changed, as the other answer says, materials, forms, and finishes may have been tweaked. The fuselage hasn't been without its issues along the way.

Going from drafting tables to CAD/CAM, structural components are among the things I would least expect to be common to the oldest and the newest 737's.

@FreeMan: You're not the only one!

@CptReynolds: A lot of the 737 MAX's basic fuselage geometry dates all the way back to the 707 (just look at the shape of the nose).


text:
Was the Space Shuttle aerodynamically neutral while piggybacking, or did the combination act like a giant biplane?
Trying to investigate this question, I see that 'Ask the Captain' says:

The weight of the shuttle is calculated like any payload. The 747
  produces enough lift to fly and to carry the weight of the shuttle. In
  this respect it is no different than cargo carried inside the
  airplane. source

But of course it is different, since cargo is generally carried inside an aircraft.
There was a fairing for the Shuttle's engines for drag reduction, but I'm wondering if the wings of the Shuttle had some aerodynamic contribution to the lifting body, or whether that was all down to the 747's wings.
 source

Related: https://aviation.stackexchange.com/questions/35305/what-was-the-space-shuttles-glide-ratio (which gives a partial answer: it costs a lot more drag to get a unit of lift from the orbiters wings than from the 747s wings)

The main goal of the fairing was to reduce the turbulence in the wake of the Space Shuttle to maintain the yaw authority of the vertical tail.

If the shuttle does produce lift, then that raises the question of whether the wings of the 747 are in the wash of the shuttle.

I instinctively feel it would handle more like a small monoplane carrying a shipping container, than a biplane!

@ROIMaison That the fairing wasn't entirely successful in this regard is demonstrated by the addition of extra vertical stabilisers (although I don't remember whether those were articulated; I'd guess probably not).

@ROIMaison: It was probably helpful, but it can't have been necessary, given that the SCA could safely be flown with a shuttle orbiter on top sans tailcone (as was done during the later Approach and Landing Tests).

This podcast with one of the pilots answers just about every question on the shuttle carrier you could have and it's worth a full listen. But to cover the flight dynamics, I would skip to 50:33 minutes, where the pilot states (please note there is no official transcript of the podcast and I typed this as I listened to it, please see the official podcast for the actual verbiage, but this is close):

Markus Voelter (Interviewer): Let's talk a bit about the flying characteristics, did the wings of the shuttle add some extra lift or
  was it mounted with essentially 0 angle of attack?
Arthur C. “Ace” Beall (Pilot): It was mounted with some angle of attack, you can see that as it's sitting. At the speed we were flying,
  the carrier itself was about 5 degrees nose high. The shuttle was creating lift, but
  how that affected it aerodynamically is hard to say, it was always
  mounted the same way so we had no basis of comparison. It did, however,
  create a lot of drag and made the aircraft very top heavy so bank
  angles were limited.

So some lift was generated but at the speeds they were flying, other limitations came into play that were more of a concern. It's also worth noting that when in transport no one was in the space shuttle and the control surfaces were not used in any way.

Given that the Shuttle had to maintain a high angle of attack while landing (at 200 mph or so), 5 degrees would likely be insufficient to lift the shuttle's weight, so the overall effect would be still that the 747 was carrying the shuttle rather than the shuttle lifting itself.

@Skyler i added a bit since there may have been a misunderstanding. The carrier its self was 5 degrees nose high and the shuttle had further positive angle of attack due to its mounting. But i agree it provided little lift in the situation.

While no one was in the orbital shuttles during transport, Enterprise was crewed during the "captive - active" portions of the Approach and Landing tests, and of course the ones where it separated and landed on its own.

The angle of attack of the shuttle and positioning of its wings looks like it might interact with the main 747 wings, neutralising any effect, something like ground effect. For sure a model of this would have been in a wind tunnel, just a matter of whether they instrumented the mounts.

Interestingly enough, for the orbiter separation maneuver to work, the Shuttle would need to have a higher lift to weight ratio than the carrier 747.  Plenty of people were probably wringing their hands (including me) over the possibility of the orbiter hitting the V stab
upon release, but when you see the video, it isn't even close.
This was accomplished with an lighter unloaded orbiter set at a higher angle of attack than the 747.  At adequate airspeed, it simply lifted away.  The higher AoA tolerance of the delta added to the safety of the manuever.  I would imagine they spoiled to lift of the 747 a little too.

Looking at https://www.youtube.com/watch?v=cOmemZl4k1U, it seems the SCA did a bit of a dive to help with separation.

@EugeneStyer, it had to do that so the orbiter would maintain speed by gliding; otherwise it would immediately start slowing down and hit the tail. Unfortunately the video is not clear enough to see whether the carrier has spoilers deployed (I would expect it does).

The L/D ratio of the Shuttle is notoriously bad, I'm pretty sure it's lower than that of the 747. So the 747 would have to dive away to separate from the orbiter.

@Hobbes, yes at equal AOA deltas are inferior, however, the Shuttle was mounted at a higher AoA.  The 747 may have idled back at separation, and may have had some flap down.  Amazingly, at separation, drag per area was very close, resulting in a very smooth release with little difference in speed.  The lift of the delta at higher AOA, combined with lower weight of an empty shuttle, did it.

@Robert, re "Amazingly", you mean, almost as if they engineered it that way?

They nailed it.  Need to find out if AOA of shuttle was set a little higher for glide test than for routine transport.

@RobertDiGiovanni It was.  From https://www.nasaspaceflight.com/2012/04/space-shuttle-enterprise-the-orbiter-that-started-it-all/ -- the relative AOA for the approach and landing tests was 6 degrees, which was reduced to 3 degrees for ferry flights.

This longer video of the first separation test shows the 747 executing a "pushover" (dive) maneuver just before separation: https://youtu.be/v-YNcwc1ZME

The space shuttle's wings are small, but they still act like wings. Their lift depends on the actual angle of attack. The space shuttle cannot be neutral for all angles.
The engineers had a choice at which precise angle to mount the space shuttle on top of the carrying 747. I would assume that the shuttle is rather close to neutral at cruising speed, to avoid excessive drag. Then it will contribute to the lift when the combination has a larger angle of attack like during start and landing.
Yes, this is a huge biplane, but the "upper wings" are designed for returning from earth orbit and landing, not for contributing much lift to the 747 combination.

This answer is speculation and assumptions. In fact, the bit about the purpose of the orbiters wings is just wrong. The orbiter's wings were designed to provide cross-track maneuverability so that the shuttle could land after a single orbit polar mission, during which the Earth would have already rotated almost two hours out of phase from it's reentry path.

@dotancohen You are welcome to share your knowledge and contribute a better answer. I would also appreciate if you let me know which of my assumptions are unreasonable. To what extent is the single orbit requirement relevant for this question?

I don't have a better answer to give. Bogl, you're not a new user, you know that speculation is frowned up here. As for the single orbit requirement, that is the basis of the orbiter's wing design. Upon reentry from a single polar orbit it would have to maneuver over a thousand kilometers off the reentry course in the atmosphere to line back up with the launch location. The wings and that huge vertical stabilizer provide the control authority to do that. Without that requirement those control surfaces could have been much, much smaller and lighter.

It's neither speculation nor assumptions.  Cold hard facts from top to bottom.


text:
Why are three-bladed helicopters relatively rare?
I admit that this observation is entirely subjective, but it seems to me that there three-bladed rotors are significantly less popular than two or four.
Factors that I'm guessing contribute -

Storage - two-bladed helicopters take up a lot less space. So you're probably going to stick with two blades until you're compelled to move to four
Simplicity - while an odd number of blades can be perfectly balanced, it may be easier to manufacture systems where the forces counter-balance in opposition rather than having to balance the entire system.
Cost - two slightly longer blades are presumably a lot less expensive to maintain / purchase than three shorter ones.

These are guesses though. My question is - is my perception correct, and if so, why?

Three bladed helicopters aren't rare.  Many European small helicopters are three bladed:

Eurocopter Fennec
Eurocopter AS355
Eurocopter Écureuil
PZL SW-4
Kamov Ka-226- it's coaxial, but still... Kamov has mostly used three blades for its coaxial helicopters.
Most of the early small helicopters by the Mil Design Bureau also had three blades, rather than two or four.

The Eurocopter helicopters show a pattern.  They are developed from one another and trace their lineage from the Aérospatiale Alouette II, III and Aérospatiale Gazelle- all with three blades.
Most American smaller helicopters have teetering rotors, which default to two blades.  This has been the case from Bell 47 to Bell UH-1 Iroquois. Here again, the UH-1's transmission system was a development of the Bell 47. Again, if you're in US (or for training generally) , you'll be seeing Robinsons, so it appears that there are almost no three bladed helicopters (with Schweizer 300 being an exception).
There are advantages and disadvantages in having different number of blades. In general, the fewer, the better. You pay for more lift, performance and (usually) less noise with mechanical complexity and less efficiency. It's a trade off.
Three versus four blades shows a clear geographical difference, due to the availability of engineers and their differing experience.

In the U.S., Enstrom Helicopters (from my hometown) are all 3-bladed designs.

I wonder if it's more for redundancy, at least in military aircraft. Not sure if that would even be a thing in helicopters, though.

@WayneWerner Almost certainly not. Losing a blade is a catastrophic event whether you have 2 blades or 6 blades.

It would make for an interesting engineering challenge: how do you construct a 4 bladed rotor such that the loss of one blade causes the opposing blade to detach safely? I suspect that it's possible by having a single attachment for the pair of opposing blades, and to have this snap when there's too much of a shear force.

@MSalters Safely is the key word there, how do you prevent other blades from coming around and smacking the ejecting blade? How do you make the ejecting blade not travel for miles as a large missile? How do you deal with the sudden (and dramatic) loss of lift? What happens with a partial blade loss (more common)?

@Ron: Mostly by not dealing with these issues. One blade crashing to earth beats an entire helicopter coming down; a sudden loss of 50% of the lift beats a sudden loss of 100% of the lift. (Not to claim that the net loss would be 50%, though). The main risk is whether a partial blade loss is better than a loss of two blades, and that probably depends on whether you typically lose 10% or 90% of a blade.

Even the Boeing CH-47 Chinook is three-bladed, in a manner of speaking.

@zelanix You're correct- I was too focused on smaller helis and missed that.

@MSalters: Loss of any significant fraction of a blade is going to be catastrophic unless one can jettison the failed blade and its counterpart quickly without damaging the other blades.  On the other hand, there aren't a whole lot of situations where a helicopter would lose one blade that wouldn't be likely to destroy all of them in short order even if a pair of blades could be jettisoned.  The only situation I can think of where the ability to jettison blades might be useful would be if a sky crane that needed to be able to lift much more than its own weight might have to make...

...an emergency landing without much clearance, but would be allowed to drop blades on whatever happened to be below.  If such a craft had two long blades suitable for lifting cargo, and two short ones suitable for keeping the craft itself aloft, jettisoning the long blades might reduce the clearance required for landing.  That would seem like a very rare situation, though.

@supercat: "On the other hand, there aren't a whole lot of situations where a helicopter would lose one blade that wouldn't be likely to destroy all of them in short order even if a pair of blades could be jettisoned" - Fatigue failure of a blade, which (IIRC) accounts for the majority of helicopter blade failures (and non-helicopter blade failures, for that matter) not resulting from direct foreign-object damage, would be one such situation.

@Sean: If a blade were to fail from metal fatigue, how long would it take for the resulting imbalance to destroy the bearings?  Would there be any plausible scenario where the failed blade and its counterpart could be safely jettisoned without failed pieces damaging other blades?

Like with propellers, the blade count on a helicopter rotor is a matter of disk loading. Light helicopters get away with fewer blades. Complexity and losses increase with blade count, so helicopter designers try to fit as few blades as possible. However, this would result in huge rotor diameters for heavy helicopters. There are reasons to keep the diameter small:

Blade root loads due to centrifugal forces
Tip speed: The advancing blade will experience transsonic effects earlier if the helicopter flies in cruise the larger the rotor is. This will limit top flight speed.
Blade bending on the ground. The blade needs to be stiff enough to clear the tail when the rotor spins up.

Now let's compare a few helicopters. I used the technical data on the linked Wikipedia page and divided the maximum take-off mass by the area of the rotor disk:

Sud Aviation Aloutette II: 2-bladed rotor. Disk loading 19.6 kg/m². Disk loading per blade: 9.8 kg/m².
Bell 205 / UH-1D. 2-bladed rotor. Disk loading 25.6 kg/m². Disk loading per blade: 12.8 kg/m².
Aérospatiale AS-350 Écureuil: 3-bladed rotor. Disk loading 25.07 kg/m². Disk loading per blade: 8.36 kg/m².
Bell 412: 4-bladed rotor. Disk loading 34.6 kg/m². Disk loading per blade: 8.65 kg/m².
Sikorsky S-65 / CH-53: 6-bladed rotor. Disk loading 50.2 kg/m². Disk loading per blade: 8.37 kg/m².
Mil Mi-26: 8-bladed rotor. Disk loading 69.6 kg/m². Disk loading per blade: 8.7 kg/m².

I guess you see the trend by now. The UH-1D is the odd man out, but it also stands apart due to its unusually high blade chord. Normally, the ideal loading per blade seems to be between 8 and 9 kg/m², and a little more is deemed acceptable if it allows the designer to get away with only 2 blades.
There is no conspiracy to suppress three-bladed rotors. It's the overall compromise between performance and efficiency which determines the number of blades on a helicopter rotor, and the main driver is mass.

Helicopter rotors have blade hinges, propellers do not. The blade root bending moment of propellers is a structural design limit that rotor blades do not have. Blade loading is not a main designparameter in helicopter rotors.

@Koyovis Then please explain why a Mil-26 cannot simply use a two-bladed rotor.

Because the whoop whoop of the blade passing noise of the Bell 212 is bad enough.

@Koyovis: Blade loading, in other words. Agreed.

An interesting statistical trend for sure. +1.

Interesting your explanation. But seems like there is inaccuracy here. According to Wikipedia [ https://en.wikipedia.org/wiki/Disk_loading ], the max. gross weight VTOL=27,400 kg, its disc area both rotors=211.4 m2, and its disc loading=129.63 kg/m2. The MV-22 is two rotors with three blades each rotor and 38-ft rotor's diameter. So, what is the explanation, what factors make of such small rotor can lift so heavy load?

While the above answers have some correct points, they miss the fundamental points of the structure and function of the rotor hub differences in the two and four blade rotors versus the three blade rotors. Both have safety issues that are nuanced, and the difference can change the mission for a given helicopter.
Two and four blade rotors are most likely semi-rigid rotor hubs that are cantilevered off a fixed pin. That allows them move free up and down through the rotation that occurs from lead and lag forces. The limitation for these rotor hubs is that it has almost no tolerance to negative G-forces because negative Gs lead to mast bumping and airframe damage in air. Pushovers have to be very subtle. This requires special training specific to SFAR 73.
Three bladed rotors have a fully articulated rotor head, which prevents mast bumping, so it has greater agility and can handle external cargo. These rotors handle lead-lag forces through hinges at the root of the rotor blade allowing the blade to move forward and aft relative to the direction of rotation throughout the revolution. The primary safety concern in these helicopters is touching down too hard or off balance jarring blades out of balance. If they do, gyroscopic forces react through the airframe, and if the helicopter is still touching the ground, that part touching the ground becomes the pivot point around which the airframe gyroscopic forces act flipping the helicopter over that pivot point. This is more likely on the three-bladed helicopters with skids instead of landing gear. The skids have shocks essentially to prevent the jarring, but if they're bottomed out or flat, the forces go through them unevenly. Helicopters with wheeled landing gear have less issue with that. Here is a good resource about fully articulated rotor heads.
Above 4 blades is when helicopters are looking to reduce noise, balance performance (both lifting capability and agility) and stability; and keeping the frequencies out of the pilot PIO and human factors frequencies become bigger issues.

The Schweizer 300 has a fully articulated main rotor head. In training, it honestly comes down to the fact that the Schweizer can tolerate heavier students than the Robinson R22 (semi-rigid main rotor head) and still be close to the same price. It's been about 10 years since I have worked on them, and I would suspect that parts are even harder to come by.

It's not clear which answers you consider "above", since user display order is selectable.  It's better if you link to specific other answers, or remove the reference entirely.

In addition to the reasons stated in the other answers, there is still a bit more on the subject. Often, the number of blades incorporated into a rotor design is about blade/disk loading, load carrying, speed-performance. Many times the number of blades is driven by vibration / ride quality and noise.
In the case of 3 blade systems, rotor vibration and noise have multiples of 3/rev, 6/rev, 9/rev. 2 AND 4 bladed systems have multiples of 2/rev, 4,rev, 8/rev, 12/rev. Odd numbered systems rarely exhibit submultiples great enough to be of concern, while even numbered systems can cover the spectrum. Think 5 vs 6 blades. The 5 bladed MD500s are almost on par with fixed wing ride quality when properly tuned.
On the other hand, take the Bell 214/214ST. A big 2 bladed example. Even with nodal beam suspension to mitigate 2/rev, these beasts ride very harsh and can only be tuned for hover and one nominal cruise airspeed.
Regarding the subject of noise. In the late 80s Los Angeles County Fire Dept, against the better judgement of the pilots, were mandated to change from the 2 bladed, Bell 205A-1 merely for the reason of noise. They subsequently bought 4 bladed, Bell 412s who's performance numbers, on paper, were stated to be equal if not marginally better. The pilots always preferred the performance characteristics of the 2 blades systems. Been on many max gross takeoffs with LACO Fire from Barton heliport, in 2 and 4 blade ships. The pre-takeoff briefing in the 4 blade 412 was not without reference to the possibility of having to pickle the load during translational lift.

To expand on the issue of noise... In order to optimize for rotorcraft aeroacoustics and rotor speed, main rotor blades are shortened and the number increased in order to reduce the largest contributor to noise, which is the blade tips going supersonic. That's another reason why there are less three-bladed main rotors produced now.


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Who picks up when you call the "phone number for you" following a possible pilot deviation?
Related - What should you do when ATC gives you a number to call to discuss a violation?
As a pilot, whom might you expect to be speaking to on calling the telephone number provided by ATC? Is it ATC themselves or do they file a report for the issue to be dealt with elsewhere?
It does seems surprising that they aren't telling you to expect to be contacted, if it's deemed an important safety issue.

In most cases the number ATC gives you will be for the recorded telephone line into the operational area—likely the supervisor's desk. If they say "possible pilot deviation" it is almost certainly going to be that recorded line. Probably they have already started filling out a Mandatory Occurrence Report for whatever situation prompted the Brasher warning in the first place.
When you call you will likely talk to the supervisor on duty, who may well be a different person than anyone who was working at the time of the incident. They will take down your name, pilot number, and a callback phone number and add them to the MOR. Eventually the FSDO will get the paperwork and an Aviation Safety Inspector at the FSDO will call you back.
In theory all that should happen when you call ATC is you give your information and they write it down and say "Thanks, you might get a call from the FSDO in a few weeks." But it's possible ATC might try get into more of a discussion about what happened. It's probably best for you to politely avoid engaging; keep in mind that the call is being recorded.
It's also possible ATC might give you the non-recorded telephone number if they just want to have a discussion about something without making it a big deal. If they say the phrase "possible pilot deviation" it's almost guaranteed to be recorded; if they don't say that phrase it might not be, but unfortunately you don't really have a way of knowing unless you ask.
Remember that you should always file an ASRS report if anything safety- or compliance-related occurred. That's the point of the "possible pilot deviation" phraseology: to inform you that ATC thinks something happened and that you should probably make a note of it so you can tell your side of the story later.
If you're interested in reading about what kinds of things are mandatory reports for ATC, they're listed in Appendix A of FAA JO 7210.632.

At Denver Center, we'll give you the number for the Operations Manager, who has the front desk in the control room. Our crew supervisors answer to them.
By the time you call, they will have looked over the situation and spoken with the controller and the crew supervisor, and will have a thorough understanding of what happened, from the ATC side.
They're not out to get you, they just want your input on what happened. Often, if it's an issue of misunderstanding, that'll be the end of it.

Air Traffic Control is who you are calling.  They are gathering more information about what might have occurred and a phone call is an easy way to do that.
Realize that first-off you are likely busy at the time, flying an airplane, so they don't want to have a discussion right then (except to correct an immediate safety situation ie "go around").  Second, they probably don't know WHO to call and might not know where you are going or when you will be available.  (They initially just know that you are Cessna-123 etc).  They could start pulling records (aircraft registration, flight plan, aircraft rental agreement, other ATC tapes....) but they often start by trying to have a conversation, then determine next steps.


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Behavior of air over a wing
Venturi´s effect states that air over the wing accelerates and static pressure drops. There's a different theory which states that as air is viscous, once it impacts the wing, slows down... Can those two theories coexist?

Yeah, air behaves very differently at sub and supersonic speeds.

Venturi effect is not actually applicable to a wing. It works with pipes. But Bernoulli's principle still applies.

Yes. In different regions.
A fluid flowing through a constricted section of a tube undergoes a decrease in pressure, which is known as the Venturi effect. This is a consequence of Bernoulli's principle, which says that total pressure is constant. Basically,
$P_{1} - P{2} = \frac{\rho}{2} (v_{2}^{2} - v_{1}^{2})$
along a streamline. But here's the catch- it is applicable only for steady, inviscid, incompressible flows. This condition is satisfied when the flow speed is small (subsonic) and at a certain distance from the body (i.e. wing) and can be used to calculate the velocity or pressure fields at some distance from it.
However, in real world, the fluid (i.e. air) is viscous, though its effects are restricted to a certain region immediately near the body, as seen below:

By F l a n k e r - Own work, CC BY-SA 3.0, Link
You can see that in the immediate region of the immersed body, the fluid is slowed down- there is a velocity gradient between the different layers of the fluid as they are being slowed down. However, after some distance from the body, the fluid behaves as if it is inviscid- there is no velocity gradient.
In the end, we choose the situation that is more useful for us- in case of subsonic flow, for calculating lift etc. the flow can safely be assumed as inviscid, while the boundary layer is very important when we consider cases like heat transfer etc. There is nothing right or wrong here (the air follows the same laws, wherever it is)- it is simply the case of using the theory that makes more sense for easier understanding and computation.


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Do pilots ever increase the cabin altitude intentionally?
Is it true that some pilots increase the cabin altitude slightly to calm down potentially disruptive passengers for safety reasons? For example, footballers who have just won a championship.

I've never heard of this "trick" being used or recommended, although the limits of what I've heard are pretty much limited to US commercial aviation.
If you climb the cabin from the usual 8000' to 10,000', the incremental gain in "sleepy" factor is a little bit but not all that much.  If you climb it above 10,000', then you might "encourage" a few of the more tired/drunk/elderly folks to go to sleep, but now you're into the realm of operating outside of normal practices, and you need to start considering things like, the pilots both need to be on oxygen, the flight attendants may get "tired" quicker than the passengers do, anybody who is elderly or in poor health may start suffering consequences, and then there are company policies and national regulations to consider.
If you raise the cabin above about 14,000 - 15,000' depending on your specific aircraft, then you'll end up activating the automatic passenger oxygen masks, and now you've got some serious 'splainin to do!  (#1, it's a bunch of work for maintenance to repack them, and the aircraft is grounded until they do, and #2 you open yourself up to all sorts of issues if you still have a long way to fly at high altitude to get to your destination!)
I'm going to guess that in the history of aviation, this sort of trick probably has been used at some point, but the opportunity for the uncomfortable questions along the lines of, "okay, tell me again, you did what exactly???" to which the best available answer is along the lines of, "um, well, it, ah, seemed like a good idea at the time, sir..." is awfully high.
I certainly wouldn't recommend it.

In addition, for most modern aircraft, this would also imply taking manual control over the outflow valve. Now, controlling the outflow valve is pretty much what you'll do for the rest of the flight. In addition to masks dropping at 14,000', you also have pressurisation warning systems which will trigger considerably earlier (10,000').

I remember reading of this "trick" in Over The Hump by Lt. Gen. W. H. Tunner. But that was unpressurised military transport, seriously unruly Chinese recruits, and the pilot claims he took them up to 24,000 ft. He might have exaggerated a bit, but not that much as their normal cruise altitude was 19,000 ft and that did not appear to affect the passengers that much (only crew had oxygen, but pax from Chinese side were acclimated to about 7,000 ft).

Not that someone may not have tried it, but it would be a patently bad idea, most likely resulting in the opposite reaction.
One of the major symptoms of hypoxia is aggression:

Behavioural changes. The person may become more verbally and physically aggressive. They may also have issues with disinhibition (ie. “socially unacceptable” behaviours). *

Add to that:

Difficulties with executive functioning , such as reasoning, judgement, initiation and impulsivity.

and your problems might get worse.
* Brain Foundation Victoria Ltd Hypoxia Information Sheet  [.pdf]

Yes, it is true that some pilots do this for that exact reason. If you're literally asking if it ever happens, you will have difficulty finding documentation, so I can only tell you what I have heard from a an aviation college professor who has claimed to have done this for the very reason the asker is describing.
When I was in college, one of the professors who would fly on behalf of the university, told us about a time that he did this to get the basketball team to calm down.
Whether or not it works, I do not know, and I have never done it nor would I because it is unethical.

You can down-vote, but it doesn't make it untrue.  Sorry if you don't like it, but in your defense, I meant the basketball team, not the football team.

Downvoted because we're looking for answers, not anecdotes and especially not anecdotes where the teller can't even remember the details.

One anecdote is hard to give much credibility, especially when no specific details are given, the original teller appears to be the coach who is certainly not an expert, and one of the only details "fresh air travels from front to back" is not true (see http://aviation.stackexchange.com/questions/1672/how-effective-are-modern-aircraft-at-clearing-smoke)

The professor who was flying the plane is not a coach... He is a commercial pilot and tenured faculty professor in the aerospace department of a state university who also does the piloting on behalf of the university.  Some down votes aren't the end of the world, and the information may be useful to someone, but if you really have a problem with answers that aren't textbook, then downvote the question that is requesting the kind of information that people don't document. There isn't a "Pilot Guide: How to Get Your Rowdy Passengers to Calm Down by Making Them Hypoxic".

@CodyP regarding air flow: thank you for strengthening the knowledge-base of stackexchange.  Of course nothing in vehicle design is a 100% guarantee, and I will be more careful in the future when I make blanket statements.

@RyanMortensen I guess if this were posted as a comment (rather than an answer), it would not have attracted so many down votes.

...but it is an answer, and clearly the OP didn't dream this question up on his own. I am sure he heard it from someone, which would only further indicate that people have attempted this somewhere and I am not necessarily providing bad information.


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What is the big hole at the bottom of the vertical stabilizer on the Boeing 717?
What is the big hole located on the forward vertical stabilizer's bottom used for?
(Image source)


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Was there really a wide gap between the performance of the F-16 similar contestants in the Lightweight Fighter Contest?
Five manufacturers submitted proposals – Vought's V-1100, Lockheed's CL-1200   the Boeing Model 908 and the F-16 and F-17. The F-16 turned out to be an agile dogfighter with "superior acceleration, climb rates, endurance, and (except around Mach 0.7) turn rates"(Wikipedia). Given that the Boeing and Vought designs resembled the F-16, would it be fair to assume that their performance would have been quite similar? Answers would have to be based on the specifications as well as a guess as to agility in combat.

The YF-17 looked a lot (lot) like the F-18. The Boeing design somewhat resembled the F-16, but I can't see much similarity between the F-16 and the V-1100... Maybe you are thinking about the Vought V-1600/1601? The V-1600 was supposed to be a Navalized version of the F-16, so its performance should be on-par with the F-16.

Suggest you read The Pentagon Paradox as background to this question even though it is a direct criticism of the F-18 buy, not the F-16 buy.  The High Low Mix was another DoD fantasy in the world of procurement, the same mentality that has brought us the F-35.  Some things do not change.

Ron, the Vought V-1100 looked similar to the F-16, with a high wing, however other images I just found here http://www.afwing.com/intro/f16_talk/f16_viper/f16_viper-6.htm shows a longer wing. Also, the Boeing model 908 has a swept wing as far as I can see from the image. Thanks.

Kovin, thanks for the link. Where can I find more information on the war scenarios where the F-16 was planned to be used in? What about the F-35? Thanks.

GD and Northrup won the contracts to build the prototype F-16 and F-17 based on a proposal package.  Since it was nothing but paper, it's hard to say how the competing designs would have fared.  In a government procurement, proposals are evaluated against criteria (technical, managerial, cost) that are provided to the bidders in the request for proposal. A badly written proposal can kill a good design. Here's a recent article on the F-16/F-17 competition.


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How to proceed in designing a catapult glider with maximum flight distance?
As a basis for this question, take the following catapult glider:
http://www.guillow.com/spaceshuttle.aspx
This model has low aspect ratio wings, a thick wing section and a relatively wide fuselage, however the surface of the glider is smooth. Is this an optimum design for distance or is there a better design possible?
How will the following parameters affect how well the glider fulfils its requirements?

Weight
Wing area
Wing planform
Fuselage width
Surface roughness
Aspect ratio

(covered here How does chord length affect wing design?)
At least what areas should a designer experiment with in order to achieve long flights?

It will all be a function of drag to lift and stability. I would make the assertion that a "flying wing" type design would probably be the best here, but i have nothing to back up that claim. I'm not sure this is even a valid question in this format, as I dont believe it is truely "answerable"

The question if the model shown is the optimum is answerable, I would think, some ways in which it could be improved, for example streamlined and given a higher aspect ratio wing might be some of the answers.  There is a related answer here: https://aviation.stackexchange.com/questions/13609/how-can-you-calculate-the-gliding-distance-for-a-remote-controlled-jet?rq=1

Two parameters are important to arrive at a good answer, but not covered in your question:

What is the size of the glider? The Shuttle model will fly at Reynolds numbers in the order of a few ten thousands, which puts it in a flight regime quite different from that of large, man-carrying aircraft.
How much kinetic energy will be provided at launch? One advantage of the Shuttle model is its large volume relative to surface area. This allows it to start the glide with more kinetic energy when compared to the model of, say, a glider. In the end, it is more ballistics than aerodynamics which can explain the gliding distance.

The optimum configuration will change with the absolute size. Aspect ratio will grow with size, and a high ratio of mass to surface area will yield better results. The Shuttle model has a weak spot, however: Its large base area will result in flow separation and high base drag. A streamlined body should be better at all sizes.

I decided not to edit the question since the meaning will be lost. In order to avoid being put on hold I really need to head for the help section, write and edit the question about 10 times and then ask.  One rule should be 1 question only.

Peter,  I am sorry the model size is not given I expect it to be of 20 cm wingspan or so. Catapult launched models in level, slowing flight is an interesting problem but I am not sure how to ask the right question here. Isn't there a trade off between mass and flight distance? Again a complex question. And you are right of course about the shuttle tail - the real shuttle has a large streamlined cover that is used when it is transported (shuttled?) back to base on a suitably modified 747.

@stackex555: A delta wing is stable in pitch; with a higher aspect ratio and less sweep you need a separate tail. An important point is whether the kinetic energy at launch is limited, or if you can make the model as heavy as you like and only the launch speed is prescribed. Too heavy and lift-induced drag will down the model, but too light and friction will stop it too soon, so there is an optimum. With 20 cm wingspan, a shuttle-like geometry can be made much bigger and heavier than the model of a regular plane, so are you free regarding length and mass?

The delta wing model I used, actually a semi scale model of a Mirage 111, would fly a short distance, pitch up (probably stall) and then continue in a downward soft of a glide. It weighed about 20 g. Lighter similar models do not have this problem, however I am wondering whether it is due to lack of elevator effectiveness or lack of lift I really find it difficult to think how I could tell the difference.

Peter, to answer your questions - kinetic energy is limited, using 2 rubber bands on a catapult and I do not intend to increase this, I am actually trying to develop a plan for a child's toy. I think I can decrease the weigh down to 10g and it will fly better, durability requirements make a lighter model unlikely. My final aim is 1:50 scale models of actual jet fighters, so my options are limited.. so much to discuss can this be moved to a discussion?

@stackex555: Your problem is the location of the center of gravity. Add some mass to the tip of the model until the flight path is straight over the full distance. What you observe is the phygoid motion of the model.

I have since built successful model gliders that can fly 20 metres  or more, which is more than enough for the small space I have. These use thin wings of cardboard from a cereal box for example and weigh between 15 and 20 grammes. A cylindrical fuselage with a nose cone is used, and the correct cg which requires slight up elevator is best. The model is a semiscale model of a Mirage 3, 1: 48 scale.ll


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What useful data can be obtained by using building and flying a scale model of a fighter aircraft design?
The use of scale models in the design of modern fighter aircraft seems to be rare, wind tunnel models and software is used instead. Is building and flying a scale model of a jet fighter or trainer design an out-dated practice?
NASA tested the HIMAT concept in the 1990s.
HIMAT concept.

While scale models may teach us a lot about flight characteristics, I would imagine that scale models are not used because wind tunnels & CFD have improved so much, even over the last 20 years, that building & flying scales is too expensive and time consuming in comparison.

Not only about fighters, since NASA built a blended wing body airliner concept. The use of flying scale models is more or less unheard of in designing civillian airliners.